My best guess at a glance is there's a JSInterop call being made either during OnParametersSetAsync or maybe OnInitializedAsync. If it's not in your pages, try removing the 3rd party components. If it's being prerendered, JSInterop calls can't be made during those lifecycle methods. I suspect the 2nd error is due to some setup changes, the Routes component can't be found for some reason.
I recommend creating a few sample solutions with the new Blazor template to see the differences. For example, create a solution with Interactive Auto and interactive per page/component -vs- Interactive WebAssembly with Global interactivity. You'll see how the Routes component is placed in the client when it's intended to be a WebAssembly only app.